1. Field of the Invention
The present invention relates to a fluorescent microscope using small light emitting elements such as a plurality of LEDs as a light source.
2. Description of the Related Art
Fluorescence observation is widely known in which particular molecules of a biological cell are visualized and distribution of its molecules can be observed.
A fluorescent microscope has been known as a microscope for the fluorescence observation which applies illumination light (excitation light) only having particular wavelength components to a specimen to observe fluorescence produced in the specimen. A mercury lamp, halogen lamp or the like is used as a light source of the illumination light in the fluorescent microscope, and a wavelength selection filter called an excitation filter is used for the illumination light emitted from the light source to extract the particular wavelength components of the illumination light, which are applied as the excitation light to the specimen.
The fluorescent microscope as described above requires space to mount various filters, and these light sources of the illumination light are large and generate large amount of heat, and thus are not easily handled.
Recently, high-luminance light emitting diodes (LEDs) have been developed as small light emitting elements, and the LED emitting white light, among others, has come into use as the illumination light in various fields. Moreover, some LEDs are monochromatic and various emission wavelengths are available, so that they tend to be used as the light source of illumination light in the microscope such as the fluorescent microscope. The use of LEDs as the illumination light source of the microscope allows many advantages to be expected, such as elimination of maintenance, smaller illumination devices, lower power consumption and a reduction in heat generation, by taking advantage of a small size, longer life and low heat generation which are characteristics of the LEDs.
Jpn. Pat. Appln. KOKAI Publication No. 2001-154103 discloses the use of LEDs as the illumination light source of a microscope, wherein an array of white LEDs is used to eliminate various adjustments during exchange of lamps, and a changeover between bright field/dark field observations of the microscope can be carried out by changing lighting parts in the same LED array, thereby obtaining an illumination device which saves space and provides satisfactory operability. Jpn. Pat. Appln. KOKAI Publication No. 2002-131648 discloses that a wavelength band of about several tens of nanometers of a monochromatic LED is used for illumination in a fluorescent microscope to realize a fluorescent microscope which does not need the excitation filter and saves space. Jpn. Pat. Appln. KOKAI Publication No. 2002-131648 further discloses that the excitation light illumination by the LEDs is implemented by a transmitted or incident-light dark field optical system to enable highly sensitive fluorescence observation with an improved signal-to-noise ratio (S/N)
On the other hand, in the fluorescence observation by the fluorescent microscope, because a sample is used which has been dyed in advance with various kinds of fluorescent dyes, an observation light amount is not sufficient due to deterioration of the fluorescent dyes over time which is so-called fading.
Thus, in order to permit irradiation of the excitation light only during observation or photographing, a mechanical shutter is disposed in front of the illumination light source, and the mechanical shutter is closed except during observation or photographing to block the excitation light so that the fading of fluorescence is reduced. The reason that the mechanical shutter is used here includes such facts that it is not necessary to open and close the shutter in a short period of time because the mercury lamp or halogen lamp used as a conventional light source requires time to relight after once turned off, and because it takes time for the lamp to stabilize its light emission.